A computer disk drive stores and retrieves data by positioning a magnetic read/write head over a rotating magnetic data storage disk. The head, or heads, which are typically arranged in stacks, read from or write data to concentric data tracks defined on surface of the disks which are also typically arranged in stacks. The heads are included in structures called “sliders” into which the read/write sensors are imbedded during fabrication. The goal in recent years is to increase the amount of data that can be stored on each hard disk. If data tracks can be made narrower, more tracks will fit on a disk surface, and more data can be stored on a given disk. The width of the tracks depends on the width of the read/write head used, and in recent years, track widths have decreased as the size of read/write heads have become progressively smaller. This decrease in track width has allowed for dramatic increases in the recording density and data storage of disks.
In a magneto-resistive (MR) sensor changes in the strength and orientation of magnetic fluxes are sensed as changes in electric resistance, as an MR read head encounters changes in magnetic data, as on a computer hard drive. In such an MR sensor, the read head operates based on the anisotropic magneto-resistance (AMR) effect in which the resistance of the read element varies in proportion to the square of the cosine of the angle between the magnetization and the direction of sense current flowing through the sensor. This effect is relatively weak in magnitude, and consequently more attention has been paid in recent years to what is referred to as “spin valve (SV) effect” or “giant magneto-resistance (GMR) effect” because of its relatively large magnitude of effect.
In this type of MR sensor, the resistance of a layered magnetic sensor varies due to both spin-depending transfer of conduction electrons between magnetic layers (M1, M2) via a non-magnetic layer (N), and spin-depending scattering at the interfaces between the layers accompanying the transfer of conduction electrons. The in-plane resistance between the pair of ferromagnetic layers (M1, M2), separated by a non-magnetic layer (N), varies in proportion to the cosine of the angle between the magnetization in the two ferromagnetic layers.
In ferromagnetic materials, scattering of electrons depends on the spin on the carriers. Resistivity is proportional to the scattering of electrons. Electrons with spins parallel to the magnetization direction experience very little scattering and hence provide a low-resistance path. If magnetization of one side of this triple layer (M2) is pinned and M1 is gradually rotated from a parallel to an anti-parallel direction, the resistance of the structure increases in proportion to the cosine of the angle of magnetizations of the two layers M1, and M2. The spin valve is sensitive at low fields because the ferromagnetic layers are uncoupled, therefore a small magnetic field from the magnetic media can rotate the magnetization in one layer relative to the other.
A constant current passes through the sensing region from one electrode terminal (not shown) to another electrode terminal. The total electric resistance of the spin valve changes in proportion to a cosine of an angle between the magnetization direction of the pinned magnetic layer (M2) and the magnetization direction of the free magnetic layer (M1). When the total electric resistance is changed, a voltage difference between the electrode terminals changes and is sensed as read information.
This type of head for writing data is generally configured with two poles separated by a gap layer of non-magnetic material. A typical prior art read/write head is shown in FIG. 4. Layers are generally deposited upon one another and generally include a shield layer 54, a dual gap layer 56, which surround a Magneto-resistive sensor, called MR sensor 58, a pole piece layer, which will be referred to as the bottom pole or P160, a non-magnetic gap layer 62, a first insulation layer or I164, upon which the coils 38 lie, and a second insulation layer, usually referred to as I266, which is generally made from photo-resist material 68. The top pole 42 is next, and is also commonly referred to as P2. The bottom and top poles 60, 42 each have bottom and top pole tips 72, 44 respectively with pole write gap 76 between them. The Air Bearing Surface (ABS) 46 and the coating layer 48 are also shown, as well as a back gap 78. The top and bottom poles 42, 60, typically extend from the ABS 46 in a roughly parallel manner until the top pole 42 veers upward to accommodate the thickness of the coils 38 and insulation layers I164 and I266. The distance through which the poles 42, 60 travel in parallel before diverging is referred to as the throat height 80, and the point at which the divergence occurs is commonly referred to as the zero throat line 82.
There are several difficulties in manufacturing a write head such as the one shown in FIG. 4. The top pole 42 is obviously contoured from the zero throat line 82 as it extends backwards from the ABS 46. The precise control of deposition processes is more difficult when dealing with contoured surfaces. Difficulties are especially encountered when using advanced photolithography techniques involving very short wavelengths of light. DUV or EUV light can only be adequately focused within a very shallow range of depth. In addition, uniform thickness of photoresist material is difficult to achieve when there are variations in contour. Magnetic properties of deposited materials are also less uniform when processed onto a contoured surface. Additionally, there are typically shadow effects when attempting to do dry etch processes near tall structures, as the etching beam is preventing from reaching into the bottom of topographical features. In order to completely clean out these areas, the tendency is to over-mill certain other surrounding areas while attempting to mill these shadowed areas properly. This can lead to unacceptable defects and poor manufacturing yields.
These problems are compounded as the top pole becomes narrower and narrower in order to decrease track widths and increase data storage density. The fabrication of the top pole is, in fact, becoming a limiting factor in the quest for narrower track width. For data densities of 100 gigabits per square inch and above, the track width must be less than 0.2 microns, meaning the top pole must be also on this order of size. This requires a very narrow and tall structure, with all the associated problems discussed above, when a top pole with a contoured top surface is used.
Thus, there is a great need for a write head having a flat top pole, which is thus easier to manufacture and which can be produced with more precise control, and for a method of manufacture which produces this type of write head having a flat top pole.